# 通訊系統 W15,W16
###### tags: `通訊系統`

# Chap 9: Using Telephone and Cable Networks for Data Transmission

## Chap 9-1 Telephone Network


### Point of oresences(POPs)



### Note: The tasks of data transfer and signaling are seperated in modrn telephone networks: data transfer is done by one network,signaling is by another.

## Chap 9-2 Dial-Up Models

*　Ｍodem stands for modulator/demodulator


## Chap 9-3 Digital Subscribe Line

### Note: ADSL is an asymmetric communication technology designed for residential users; it is not suitable for business.

### NOte: ADSL is an adaptive tecknology. The system uses a data rate based on the condition of the local loop line.



| ADSL Bandwidth | 對照頻段功能 |
| -------- | -------- |
|  |  |
| ADSL modem | DSLAM |
| |  |

## Chap 9-4 Cable TV Networks

### Note: Communication in the "traditional cable" TV network can be budirectional.


### Note: Communication in an "HFC cable" TV network can be budirectional.


## Chap 9-5 Cable TV for Data Transfer



# Chap 10: Error Detection and Correction

### Note: Data can be corrupted durong transmission. Some applications require that errors be detected and corrected.

## Chap 10-1 Introduction

### Error
1. Single bit error(整個訊息錯一個以上)
2. Burst error(整個訊息錯兩個以上)
### Note: In a single-bit error, only 1 bit in the data unit has changed.

### Note: A burst error means that 2 or more bits int the data unit have changed.

### Redundancy
用於作為檢查碼(detect and correct errors)

### To detect or correct eooros, we need to send extra(redundant) bits with data.

### Detection
Only給予有錯或沒錯的回覆

### Crrection
要給出錯在哪裡，並且更正錯誤

1. Forward error corrction => 繼續傳送，並且檢查錯哪裡
2. Retransmission => 直接重傳，花頻寬

* The structure of encoder and decoder
### Note: In this book, we concentrate on(專注於) "block codes"; we leave convolution codes to advanced texts.


### In modulo-N arithmetic, we use only the intergers in the range 0 to (N-1), inclusive.


## Chap 10-2 Block Coding
先把資料切為blocks，並放入一些bits為datawords，放入k bits，並再放入r bits for redundant bits，最為codewords


### Note: An error-detecting code can detect only the types of errors for which it is designed; other types of errors may remain undetected.

### Note: The Hamming destance between two words is the number of differences between corresponding bits.

### The minimum Hamming distance is the smallest Hamming distance between all poossible pairs in a set of words.

### Note: To guarantee the detection of up to s errors in all cases, the minimum Hamming distance in a block code must be d_min = s + 1


### The guarantee correction of up to t errors in all cases, the minimum Hamming distance in a block code must be d_min = 2t + 1


## Chap 10-3 Linear Block Codes

### note: In a linear block code, the exclusive OR(XOR) of any two valid codewords creaes another valid codeword.

### Note: A simple parity-check code is a single-bit error-detecting code in which n = k+1 with d_min = 2


## 2 dimensional parity-check code



### Note: All Hamming codes discussed in this book have d_min = 3. The relationship between m data and n in these codes is n = 2m -1.



## Chap 10-4 Cyclic Codes



## Hardwared design



## Chap 10-5 Checksum